Refactor HTTP Method from Enum to Class

This commit refactors HttpMethod from a Java enum into a class. The
underlying reason being that HTTP methods are not enumerable, but
instead an open range and not limited to the predefined values in the
specifications.

Closes gh-27697

spring-web/src/main/java/org/springframework/http/HttpMethod.java

@@ -16,13 +16,15 @@
 
 package org.springframework.http;
 
+import java.io.Serializable;
 import java.util.HashMap;
 import java.util.Map;
 
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 
 /**
- * Java 5 enumeration of HTTP request methods. Intended for use
+ * Represents an HTTP request methods. Intended for use
  * with {@link org.springframework.http.client.ClientHttpRequest}
  * and {@link org.springframework.web.client.RestTemplate}.
  *
@@ -30,32 +32,131 @@ import org.springframework.lang.Nullable;
  * @author Juergen Hoeller
  * @since 3.0
  */
-public enum HttpMethod {
+public final class HttpMethod implements Comparable<HttpMethod>, Serializable {
 
-	GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE;
+	private static final long serialVersionUID = -70133475680645360L;
 
+	private static final HttpMethod[] values;
 
 	private static final Map<String, HttpMethod> mappings = new HashMap<>(16);
 
+
+	/**
+	 * The HTTP method {@code GET}.
+	 * @see <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.3">HTTP 1.1, section 9.3</a>
+	 */
+	public static final HttpMethod GET = new HttpMethod("GET");
+
+	/**
+	 * The HTTP method {@code HEAD}.
+	 * @see <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.4">HTTP 1.1, section 9.4</a>
+	 */
+	public static final HttpMethod HEAD = new HttpMethod("HEAD");
+
+	/**
+	 * The HTTP method {@code POST}.
+	 * @see <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.5">HTTP 1.1, section 9.5</a>
+	 */
+	public static final HttpMethod POST = new HttpMethod("POST");
+
+	/**
+	 * The HTTP method {@code PUT}.
+	 * @see <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.6">HTTP 1.1, section 9.6</a>
+	 */
+	public static final HttpMethod PUT = new HttpMethod("PUT");
+
+	/**
+	 * The HTTP method {@code PATCH}.
+	 * @see <a href="https://datatracker.ietf.org/doc/html/rfc5789#section-2">RFC 5789</a>
+	 */
+	public static final HttpMethod PATCH = new HttpMethod("PATCH");
+
+	/**
+	 * The HTTP method {@code DELETE}.
+	 * @see <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.7">HTTP 1.1, section 9.7</a>
+	 */
+	public static final HttpMethod DELETE = new HttpMethod("DELETE");
+
+	/**
+	 * The HTTP method {@code OPTIONS}.
+	 * @see <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.2">HTTP 1.1, section 9.2</a>
+	 */
+	public static final HttpMethod OPTIONS = new HttpMethod("OPTIONS");
+
+	/**
+	 * The HTTP method {@code TRACE}.
+	 * @see <a href="https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.8">HTTP 1.1, section 9.8</a>
+	 */
+	public static final HttpMethod TRACE = new HttpMethod("TRACE");
+
+
 	static {
-		for (HttpMethod httpMethod : values()) {
+		values = new HttpMethod[]{GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE};
+		for (HttpMethod httpMethod : values) {
 			mappings.put(httpMethod.name(), httpMethod);
 		}
 	}
 
 
+	private final String name;
+
+
+	private HttpMethod(String name) {
+		this.name = name;
+	}
+
+	/**
+	 * Returns an array containing the standard HTTP methods. Specifically,
+	 * this method returns an array containing {@link #GET}, {@link #HEAD},
+	 * {@link #POST}, {@link #PUT}, {@link #PATCH}, {@link #DELETE},
+	 * {@link #OPTIONS}, and {@link #TRACE}.
+	 *
+	 * <p>Note that the returned value does not include any HTTP methods defined
+	 * in WebDav.
+	 */
+	public static HttpMethod[] values() {
+		HttpMethod[] copy = new HttpMethod[values.length];
+		System.arraycopy(values, 0, copy, 0, values.length);
+		return copy;
+	}
+
+	/**
+	 * Return an {@code HttpMethod} object for the given value.
+	 * @param method the method value as a String
+	 * @return the corresponding {@code HttpMethod}
+	 */
+	public static HttpMethod valueOf(String method) {
+		Assert.notNull(method, "Name must not be null");
+		HttpMethod result = mappings.get(method);
+		if (result != null) {
+			return result;
+		}
+		else {
+			return new HttpMethod(method);
+		}
+	}
+
 	/**
 	 * Resolve the given method value to an {@code HttpMethod}.
 	 * @param method the method value as a String
 	 * @return the corresponding {@code HttpMethod}, or {@code null} if not found
 	 * @since 4.2.4
+	 * @deprecated in favor of {@link #valueOf(String)}
 	 */
 	@Nullable
+	@Deprecated
 	public static HttpMethod resolve(@Nullable String method) {
 		return (method != null ? mappings.get(method) : null);
 	}
 
 
+	/**
+	 * Return the name of this method, e.g. "GET", "POST".
+	 */
+	public String name() {
+		return this.name;
+	}
+
 	/**
 	 * Determine whether this {@code HttpMethod} matches the given method value.
 	 * @param method the HTTP method as a String
@@ -66,4 +167,30 @@ public enum HttpMethod {
 		return name().equals(method);
 	}
 
+
+	@Override
+	public int compareTo(HttpMethod other) {
+		return this.name.compareTo(other.name);
+	}
+
+	@Override
+	public int hashCode() {
+		return this.name.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) {
+			return true;
+		}
+		else if (o instanceof HttpMethod other) {
+			return this.name.equals(other.name);
+		}
+		return false;
+	}
+
+	@Override
+	public String toString() {
+		return this.name;
+	}
 }